The proposed research will assess the precision of caloric intake regulation in individuals presented with diets varying in caloric concentration. In particular, the study is designed to compare the effects of low- and high-fat diets on spontaneous caloric intakes of subjects consuming foods and snacks prepared with conventional ingredients. Using a Latin Square design for treatment sequence, a series of three experimental diets will be administered of foods whose ratio of calories from dietary fat to total calories falls within a specified range: 15-20%, 30-35%, or 45-50%. Precise determinations of energy and fat intake will be made while allowing subjects maximum flexibility in selection and consumption of foods. The hypothesis is that subjects will increase their caloric intake on the high-fat diet and decrease caloric intake on the low-fat diet, relative to the medium-fat diet. Variation in subjects' body types will permit an analysis of a possible interaction between adiposity and caloric regulation. The results of this study may provide evidence that a qualitative approach which specifically focuses on the fat content of the diet is a more effective means of achieving a sustained weight loss than a quantitative approach emphasizing the number of calories consumed.